(1) Field of the Invention
The present invention relates to a ball-point pen having an improved ball-point pen refill mounted therein whose writing tip may project and retract from the barrel of the ball-point pen. More specifically, the present invention is directed to a ball-point pen having a ball-point pen refill equipped with ink leak-preventing mechanisms for preventing forward and backward ink leakage when low-viscosity oily ink is employed.
(2) Description of the Prior Art
The present applicant has disclosed a back leak-preventing mechanism in Japanese Utility Model Publication Hei 4 No.52067 in which prevention of backward leakage of ink is effected by providing a valve chamber having a ball valve put therein with play. This disclosure provides a ball-point pen in which a plastic mouthpiece made of a synthetic resin having a required number of projecting ribs is provided so that the ball is held therein with play and may not slip out and, upon writing, ink flows to a tip through channels formed between the projecting ribs.
Conventionally known ball-point pens can be categorized into two types, one of which is a so-called oil type ball-point pen that uses a high-viscosity ink. The other is a so-called water type ball-point pen which includes sliver fibers holding ink therein and an ink feeder that leads ink from the fibers to the tip of the ball-point pen.
The ink of the conventionally known oil type ball-point pen has high viscosity, therefore, when the ball-point pen is used for writing, only a small amount of the ink can flow out as a tip ball rotates. Further, the ball-point pens of this type have defects such as ink-blotting, unevenness of writing traces, low writing density, requirement of high writing pressure and the like.
In contrast, water type ball-point pens use more costly materials since the water type ball-point pen uses sliver fibers for keeping the ink. Additionally, the water type ball-point pen has a drawback that consumption of ink cannot be known.
Under these circumstances, in order to solve the drawbacks of both types of the ball-point pens, a water type ball-point pen has been presented which uses water-type thixotropic ink (or having shear viscosity decreasing property) that has relatively low viscosity for canceling the defect of oil type ball-point pens and exhibits high viscosity at static state but lowers its viscosity at writing due to the rolling of the ball to thereby allow easy flow-out of ink.
However, as to the ball-point pen using such thixotropic ink, the ink of this type tends to flow out in a large amount in order to enhance the writing density and therefore the ink reservoir is made large in diameter so that it can store a large amount of ink.
Additionally, the ink having thixotropy has another defect, that is, the ink is easy to dry. Therefore, it is necessary to provide a cap especially for sealing the writing tip.
Alternatively, in order to solve the problems, use of oily ink having low viscosity and resistance to dryness might be used, but the ink of this type also tends to flow out in a large amount and in order to lengthen the life of the pen, the ink reservoir is made large in diameter so that it can store a large amount of ink.
In addition, since the viscosity of the thixotropic ink is low as compared to that of the conventional ink for oil type ball-point pens, the flow resistance of the ink in question against the wall of the ink reservoir is small. Accordingly, the ink is liable to leak backward to the rear end of the ink reservoir due to self-weight of the ink, knocking or falling impacts. To deal with this drawback, the rear end of the ink in the reservoir is generally provided with a greasy ink follower which moves following the consumption of ink during writing and inhibits the back leaking of ink which would be brought about by self-weight of ink or outside impacts. However, even with the provision of the ink follower, if the ink immediately below the tip ball is used up when the writing is performed with the pen upward, the head or pressure of the ink acts directly on the ink follower, causing notable backward leakage of ink. Besides, when the ink reservoir is made with a large inside diameter and length so as to increase the reserve amount of ink, it becomes difficult to regulate the backward flow phenomenon caused by outside impacts. Once ink leaks backward, the ink not only pollutes the barrel inside but also leaks out through the vent disposed in the barrel to pollute the user's hands and clothes. It is true that oil type ball-point pens also suffer from the backward flow phenomenon of ink but the phenomenon occurs more apparent in the case of the ball-point pens using thixotropic ink.
To make matters worse, since the ink has low viscosity and tends to flow out in a large amount, any gap between the tip ball and tip ball holding portion causes ink to ooze out (in the forward direction) from the tip when the tip is oriented downward. Further, after the pen is used to write with its tip upward or after the pen undergoes knocking impact or falling impact, the ink immediately below the tip ball tends to be drawn backward, so that subsequent writing becomes unclear.